Traveling wave electron discharge device



AugQlZ, 1958 5. J. WILLSHIRE 7,

TRAVELING WAVE ELECTRON DISCHARGE'DEVICE I Filed July 9, 1954 EWHQZBB lmjenlor S. J. WILLSHIRE Attorney United States Patent TRAVELING WAVE ELECTRON DISCHARGE DEVICE Stanley John Willshire, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application July 9, 1954, Serial No. 442,410

Claims priority, application Great Britain July 13,1953

5 Claims. (Cl. 315-3) The present invention relates to the construction and manufacture of travelling wave tubes of the helix type.

In the operation of a travelling wave tubeofthe type to which the present invention relates, an electron beam, generated by an electron gun, is projected along the axis of a uniform helix of conductive material to a collector electrode at the far end of the helix. The helix behaves as a transmission line or waveguide having low propagation velocity. By suitable coupling means an electromagnetic wave is launched upon t e helix at the electron gun end of the tube and an axial component of the wave is progressively amplified along theleng th of the helixby interaction with the electron beam. The amplified wave is fcdto a further transmission line or waveguide by suitable coupling means at tie far end of the helix. The helix is polarized to some convenient potential with respect to the cathode of the electron gun by means of a lead-in connection in the electron gun end of the tube. In some cases thehelix is conveniently connected directly to the final anode of the electron gun and shares the same lead-in connection. The collector electrode may be operated at a slightly higher potential than that of the helix, so as to avoid any trouble due to secondaryemission, or itmaybe operated at the same potential. It is not desirable, however, that there should be a direct connectionbetween the collector electrode and the helix, as it would thenbe difficult, if not impossible, to determine what proportion of the beam current was impinging upon the helix.

In a typical construction of travelling wave tube the helix is supported in a glassenvelope clcsedat one; end by the electron collector electrode andsealed at. the other end to a bulb portion provided with a conventionalvalye base carrying lead-in. connections'for the gunielectrodes and helix. Two problems arise inthe manufacture and construction of such tubes. In the first place, if there is to be no connection during operation betweenthehelix and the collector electrode, special meanshave to be provided for locating the end of the helix adjacent the collector electrode. in some designs this is accomplished-by means of an internally projecting radial ribon the envelope of the tube, which involves a carefully'dimensionedoper-ation on glass work which has already to be accuratelydimensioned in other respects to ensure alignment of the various electrodes. The second problem is that gas liberated from the helix of the tube during its operatiomhas heenfound to have a detrimental effect'on the characteristics and life of the tube. This is particularly so with tubes passing a high current density beam.

in the past several methods have been tried for outgassing the helix during processing of the tube, but none has been altogether satisfactory. To enable the helix to be raised to a dull red temperature with an A. C. or D. C. voltage source, a contact is necessary at each end. As indicated above, in preferred constructions there is a contact to the helix at only the input end.

It is an object of the present invention to provide a construction and method of manufacture of a travelling wave "ice tube which will allow simple and accurate assembly of the electrode system within the tube envelope and which will also enable the helix to be outgassed by means ofa temporary connection at the out-put as well as at the input end of the helix.

' According to one aspect of the present invention there is provided, in the manufacture of a travelling wave tube a conductive helix connected at one end to a lead-in connection, and an electron collector electrode at the other end of the helix, not connected thereto during operation, the method of outg-assing the helix by joining the adjacent end thereof. to the said collector electrode by means of a fusible link, connecting a source of helix heating current between the said lead-out connection and the collector electrode untilthe helix isoutgassed, and then applying a current surge to fuse the said link.

According to a further aspect of the invention there is provided a travelling wave tube comprising an electron gun, a wire helix along the axis of which an electron beam from the said gun isprojected, a collector electrode at the end of the helixremote from the, electron gun, a lead-in connection aLthe electron gun end of the helixawhich, if desired, may be common to an electrode of the said electron gun, a waveguide choke sleeve member intermediate the collector. electrode and helix connected to the helix, a resilient metal crown fitting inside the said collector electrode, a tube of insulating material secured at one end to the said metalcrown and at the other end fitting inside the said sleeve member, and means during manufacture. for inserting a fusible link between the said metal crown and the said helix, so that current may be passed through the helix during manufacture, the said length beingfused ata subsequentstage of manufacture to interrupt theconnection between the said helix and the collector electrode.

An embodiment. of the invent-ion will be described with i reference to the accompanying drawings, in which:

Fig. 1 shows a complete travelling wavetube embodying the invention, with connections indicated for outgassing the .helix, and

Fig. 2 shows an exploded view ofthat part of the travelling wave tube of Fig.- 1- adjacent the collector electrode.

In Fig. 1 reference numeral liindicates a glass envelope portion, housing an elcctrongun 2, sealed at one endto a longtubular envelope. portion 3 of. smaller diameter and at the other to .a conventional valve. base 3a carrying contactpins4. The electron gun electrodes are supported. in theenvelope portionl by means of insulating washers 5 secured to support wires 6 which are. mounted on a glass press 7. I

The envelope portion 3 contains a helix 8 of wire connected at its ends via waveguide probe elements 9 and 10 to respective sleeve members 11 and 12, which constitute the inner members of quarter wave waveguide chokes, corresponding outer members being fitted to the external input and output waveguides not shown. The helixfi is supported'by means of three accuratelyground glass rods 13, of which two are visible in the drawing, securedto the sleeve members 11 and lZ. .The middle of envelope portion .3 carries, preferably on its inner surface, a resistance coating. The end of the envelope portion 3, remote from the electron gun, is closed by means of a collector electrode 15 having a hollowed-out portion adjacent the region 16 where it is secured to the glass of the envelope. At the electron gun end of the tube the sleeve member 12 is shown secured to a second anode 17 of the electron gun by means of a tube 18,

which surrounds the electron beam path between the the sleeve member is seated. In the construction according to the present invention, as is shown in the exploded view of Fig. 2, a resilient metal crown member 19, which is hollow to permit the electron beam to pass therethrough and impinge on the collector electrode 15 is secured within one end of a small glass tube 20, which slides into the end of the sleeve 11.

In order to provide a fusible link temporarily joining collector electrode 15 and the helix 8, a thin metal tape 21 is secured to the crown member 19 and passes along the inside of the glass tube 20 and around the end thereof as indicated at 22, the diameter of the tube 20 being such that, with the tape intervening, a snug fit is formed inside the end of sleeve 11.

The electron gun 2, together with the connecting tube 13, the sleeve members 12 and 11, separated by the glass rods 13, the helix 8, the glass tube 20 and the crown member 19 are assembled together as one mechanical unit. This assembly is mounted upon the pinch 7 of the glass base of envelope portion 1, which has not yet been sealed thereto, and is inserted into the remainder of the envelope and pushed home until the crown member 19 seats inside the collector electrode portion 16, making contact by means of the fusible link 21 between the collector electrode and the helix. The envelope base carrying the pinch is then sealed to the envelope portion 1 and the tube is mounted on a pumping station for processing.

When it is desired to outgas the helix a suitable source of current, indicated in Fig. 1 by the battery 22, is connected between the collector electrode 15 and that one of the lead-in connections in the base of the tube connecting to the electron gun end of the helix. In Fig. 1 the tube is shown with its final base 3a carrying conventional valve pins, the tube having been sealed off; the outgassing operation, of course, will take place before the tube is sealed oh, and, therefore, before the base 3a is cemented to the glass of the envelope. The metal of the fusible link 21 is chosen so that it is capable of carrying sufficient current to allow the helix to be brought up to the requisite temperature (750800 C.) to cause the helix to glow a dull red. When outgassing is complete the helix is allowed to cool and the link is then burned out instantaneously by a sudden heavy application of current. The helix has sufficient thermal capacity to remain cool during the fusing of the link.

In a typical tube the helix was made of 0.028 inch diameter nickel-chromium wire and had a total helix length of 8% inch, while the fusible link 22 of Fig. 2 consisted of a strip of copper-nickel alloy 0.030 inch wide, 0.004 inch thick and inch long. The heating current applied to the heater 9 required for outgassing is of the order of 3.5 amperes and for the final fusing operation a current surge of 10 amperes is passed.

By means of the invention not only is it possible in the manufacture of travelling wave tubes to outgas the helix thoroughly, which in itself results in better performance and longer life, but by means of the construction described above, a more accurate location of the tube elements is achieved.

While the principles of the invention have been described above in connection with specific embodiments,

and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What is claimed is:

1. In the method of manufacture of a travelling wave tube having a conductive helix connected at one end to a lead-in connection, and an electron collector electrode adjacent the other end of the helix, the electron collector electrode being arranged so that an external connection may be made thereto, the steps of outgassing the helix comprising fusibly linking the adjacent end of the helix to said collector electrode, connecting a source of helix heating current between the said lead-in connection and the collector electrode until the helix is outgassed, and then applying a current surge to fuse and break the fusible linkage.

2. The method according to claim 1 further comprising the step of permitting the helix to cool after it has been outgassed before applying said current surge.

3. In the method of assembling a travelling wave tube having an envelope, an electron gun, a helix, a collector electrode, a resilient member adapted to mechanically fit into said collector electrode, the steps comprising forming a first assembly consisting of sealing said collector electrode to said envelope, and a second sub-assembly consisting of mounting the electron gun from the base, supporting one end of the helix from the base and mechanically connecting the other end of the helix to the resilient member; and inserting the second sub-assembly into the envelope so that the resilient member engages the collector electrode; and sealing the glass envelope to the base.

4. A travelling Wave tube comprising an electron gun, a wire helix along the axis of which an electron beam from said gun is projected, a collector electrode at the end of the helix remote from the electron gun, a lead-in connection to said helix, a waveguide sleeve member connected to the helix intermediate the collector electrode and helix, a resilient metal cap fitting inside said collector electrode, a tube of insulating material secured at one end to said cap and at the other end fitting into said sleeve member, a fusible metal link in said insulating tube for use in outgassing said tube, said metal link electrically connecting the helix, sleeve and cap and being fused subsequently to said outgassing to provide a gap between the helix and collector electrode.

5. The travelling wave tube of claim 4, wherein said fusible link comprises a metal tape connected at one end to the cap and fitting over an internal wall of said insulating tube, said link extending over the opposite end of the tube and clamped by the adjacent sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 1,456,528 Arnold May 29, 1923 2,183,952 Anderson Dec. 19, 1939 2,584,802 Hansell Feb. 5, 1952 2,660,689 Touraton et al. Nov. 24, 1953 FOREIGN PATENTS 655,164 Great Britain July 11, 1951 693,713 Great Britain July 8, 1953 

